Allergic Reaction and Anaphylaxis
Try our free symptom checker
Get a thorough self-assessment before your visit to the doctor.
What are allergic reactions and anaphylaxis?
An allergic reaction is when the body responds to something that it sees as a threat, even though it isn’t. These triggers are also called allergens. Some examples of allergens are foods, medications, dust, or pollen. A mild reaction may cause minor symptoms, like sneezing or itchy eyes. However, some allergic reactions can be severe. This is called anaphylaxis, and it can be life-threatening.
During anaphylaxis, a person may have difficulty breathing, have a rapid heart rate, an itchy rash (hives), and/or swelling of their lips, tongue, or throat. They may wheeze, cough, vomit, be lightheaded, or faint.
If having symptoms of anaphylaxis, seek help immediately—epinephrine is the best way to halt the reaction. If you have a history of anaphylaxis and have been prescribed an epinephrine auto-injector (EpiPen), use it, and then call 911.
Most common symptoms
Mild allergic reactions are often caused by allergens in the environment, like pollen, dust, mold, or animal hair and dander. They tend to affect the eyes, nose, and sometimes the lungs, especially if you also have asthma. They rarely cause severe reactions like anaphylaxis.
Main allergy symptoms
Anaphylaxis is often caused by foods, medications, latex, or insect stings. The first sign of a reaction might seem minor—you might develop hives or some mild lip swelling.
But symptoms can then progress and start to involve the heart or lungs. You may have difficulty breathing, feel dizzy due to low blood pressure, cough, or vomit.
Main anaphylaxis symptoms
You can have many different symptoms during anaphylaxis. Some of these include:
- Hives: Red, raised, itchy bumps
- Flushed: General redness and warmth of the skin
- Oral (mouth area)
- Swollen lips and/or tongue
- Swollen throat: Can cause trouble swallowing, speaking, or breathing
- Swollen eyes: Both upper and lower eyelids can be involved
- Runny and/or stuffy nose
- Itchy, watery eyes
- Gastrointestinal (digestive tract)
- Low blood pressure (dizziness, passing out)
- Rapid heart rate (palpitations)
- Chest pain
One of the most important questions you can ask is, “How can I prevent this from happening again?” The answer to this question includes figuring out what triggered your reaction and how to avoid that particular trigger. Allergists are trained to help answer these questions and help you come up with a plan that makes it as easy as possible to live with your allergy. —Dr. Amrita Khokhar
You are more likely to develop allergies or anaphylaxis if you:
- Have other allergies or allergic conditions, such as asthma or eczema (an allergic rash).
- Have an immediate family member with a history of allergies or anaphylaxis. For example, if you have a parent or sibling with food allergies, it’s more likely that you will develop a food allergy at some point.
- Take beta-blockers: Some people who take beta-blockers for high blood pressure might be more likely to develop severe allergic reactions to allergens. Beta-blockers can also make anaphylaxis more difficult to treat because they can prevent epinephrine from working properly.
What to do next
Mild allergic reactions to environmental allergens like pollen or animal dander can often be managed at home. You can take over-the-counter allergy pills or nasal sprays. If your allergies aren’t responding well to these treatments, or if your symptoms are interfering with your daily activities, your doctor can prescribe stronger medications or you can see an allergist to discuss further treatment.
But allergic reactions that occur after eating a food, taking a medication, or getting an insect sting can vary in severity. Your body’s response might be mild, like itching or hives. Mild symptoms can be treated with an allergy pill, like diphenhydramine (Benadryl).
But keep a close eye on how you are feeling in case you develop other symptoms, like swelling or trouble breathing. Sometimes even mild symptoms can progress to an anaphylactic reaction.
An epinephrine auto-injector (EpiPen) is a device that contains an age-appropriate dose of epinephrine, a life-saving medication used to treat anaphylaxis.
If you think you are having anaphylaxis, you should take the following steps:
- If you think you are having anaphylaxis but have never been diagnosed before, call 911 immediately. Epinephrine is necessary in treating anaphylaxis and should not be delayed.
- If you have previously been diagnosed with anaphylaxis or a severe allergy, you should use your epinephrine auto-injector immediately.
- Call 911 or go to the emergency room, even if your symptoms improve after using epinephrine. Symptoms can return hours after you have taken epinephrine, known as a “biphasic reaction.”
- Lie down after using epinephrine. This helps ensure you are getting enough blood flow to your vital organs, like your brain.
- You can use another dose of epinephrine after 5 minutes if you are not feeling better. Epinephrine injectors will often come in packs of two for this reason.
If you suspect you are having anaphylaxis, you should not:
- Wait and see how bad your symptoms get before using epinephrine. Anaphylaxis can rapidly lead to low blood pressure, anaphylactic shock, and even death. Epinephrine is the best medication to help treat anaphylaxis.
- Take an allergy pill (antihistamine) instead of epinephrine. Allergy pills do not help treat or reverse anaphylaxis.
- Walk around after using epinephrine. Lie flat until help arrives. This is to make sure that you do not experience any sudden changes in your blood pressure.
If you have had an allergic reaction, especially anaphylaxis, you should see an allergist. They can perform testing to help identify what you’re allergic to. And can guide you on how to manage and treat your allergy.
How to treat allergic reactions and anaphylaxis
A treatment for peanut allergy called Palforzia was recently approved by the FDA. This is a new type of treatment called oral immunotherapy, where small amounts of the food protein are given to a person to reduce their risk of anaphylaxis if they were to accidentally ingest the food they are allergic to. —Dr. Khokhar
Mild to moderate allergic reactions can be treated with over-the-counter or prescription antihistamines.
Your doctor may also give you oral or topical steroids to treat itching from hives, runny nose, congestion, sneezing, or tearing. Any of these medications may also be taken alongside epinephrine for anaphylaxis, but never in place of it.
Prepare ahead of time for an allergic reaction. Discuss with your doctor in advance how much medication to take. Know what the potential side effects are and possible interactions with other medications you may take regularly.
- Epinephrine is available by prescription and comes in prefilled injectors to make it easier to deliver. It is available under several different brand names and doses, depending on if the prescription is for an adult or a child.
- Antihistamines: Diphenhydramine (Benadryl) is usually taken for a mild allergic reaction, though it can cause drowsiness, and should not be given to elderly patients due to side effects. Loratadine (Claritin), cetirizine (Zyrtec), and fexofenadine (Allegra) can be taken during an allergic reaction or daily during allergy season to reduce symptoms. They are considered non-drowsy antihistamines.
- Steroids: Prednisone can reduce a reaction.
- Bronchodilator. You may need albuterol if you have a history of wheezing or asthma (cough, wheezing, shortness of breath). It is taken via an inhaler or nebulizer (creates a fine mist that you inhale).
When children have an allergic reaction or anaphylaxis
You can outgrow the allergy. We see this a lot in children who have allergies to things like milk or soy. Another common allergy to outgrow is penicillin. —Dr. Khokhar
Anaphylaxis can happen in children, too. Food allergy is the most common cause of anaphylaxis in children, but insect stings and medications can also be possible triggers. Allergic reactions can occur at any age.
Epinephrine can be safely prescribed to children who have had a history of anaphylaxis, or might be at risk for anaphylaxis. Children under 66 pounds will be prescribed a smaller dose of epinephrine.
Children may be given the same types of medications as adults, but most children’s medication is dosed based on weight so discuss the correct amount with your pediatrician before you give any medication to them.
Children can outgrow allergies. Food allergies, for example, can improve or go away as children get older. Regular follow-up visits with an allergist for a check-up and allergy testing are recommended to determine if your child has outgrown their allergy.
What happens in your body when you have an allergic reaction?
An allergic reaction and/or anaphylaxis is the body’s way of fighting off something it considers a threat to the body’s well-being. But, in this case, it is a mistake. The body is incorrectly treating something that is not harmful as a danger to the body.
In some cases, the allergen might be something that you have been exposed to multiple times before. For example, some people might suddenly develop an allergy to cats in adulthood, even if they have lived with cats in the past. In other cases, the allergen might be something that you’ve only been exposed to once or twice, like a medication.
The cause of an allergic reaction can vary from person to person, but there are some common allergens that cause the majority of reactions. These include:
- Foods: peanuts, tree nuts, seafood, eggs, wheat, soy, milk
- Insect stings and bites: bees, wasps, hornets, yellowjackets, fire ants
- Medications: antibiotics, pain medications
- Latex-containing products
- Environmental allergens: animal hair or dander, pollens, dust, mold, cockroaches
It is very important to follow all instructions and take all medications as directed. If you or your child had a severe allergic reaction or anaphylaxis, you will be prescribed an epinephrine auto-injector. These are prescribed in sets of two so you always have a backup.
You will often be given several refills so that they are always available in the event of an emergency. Keep a set at home, at work, at school (for a child), and on your person at all times.
Epinephrine should be kept at room temperature. It should not be refrigerated or frozen. Do not leave epinephrine in an area that can become hot, like in the glove compartment of a car or in the trunk. Periodically check the expiration date of the auto-injector and refill the prescription if it has expired.
If you have had an allergic reaction, avoid the possible trigger. You should see an allergist to help identify the trigger and to perform allergy testing if needed. They will help you create an allergy action plan. This type of plan includes preventative steps and what to do during an allergic reaction.
- Avoid triggers. An allergist can help identify your trigger through the use of allergy testing if you are unsure what caused the reaction.
- Get an epinephrine auto-injector if you have had anaphylaxis. Always be prepared and keep it with you. If you have another episode of anaphylaxis, epinephrine can be life-saving.
- Create an allergy/anaphylaxis action plan: Work with your allergist to create this. It can be very helpful for people who aren’t familiar with the common symptoms of an allergic reaction or the signs that a reaction is progressing to potentially life-threatening anaphylaxis. Share the plan with family members, friends, and coworkers. Schools often require an allergy action plan for allergic children.
Dr. Manuelpillai is a board-certified Emergency Medicine physician. She received her undergraduate degree in Health Science Studies from Quinnipiac University (2002). She then went on to graduated from Rosalind Franklin University of Medicine and Sciences/The Chicago Medical School (2007) where she served on the Executive Student Council, as well as was the alternate delegate to the AMA/ISMS-MSS Governing Council and the student representative to the Illinois State Medical Society (ISMS) Education and Health Workforce committee. She completed an internship year with UCLA-Harbor Medical Center's Department of Internal Medicine followed by an emergency medicine residency program at Boston Medical Center (2011) while also serving as the resident representative to the Massachusetts Medical Society (MMS) committee on Student Health & Sports Medicine. She then started working at Saints Medical Center (later Lowell General Hospital/Saints Campus and Main Campus) in Lowell Massachusetts where she served as the Continuous Quality Improvement Director for the emergency medicine group, as well as was the representative for the emergency department on the Sepsis, Stroke and PCI Quality Assurance and Compliance Committees. She joined Buoy Health in 2019. She currently works in multiple emergency departments both in the community and academics, as well as previously worked in multiple urgent care centers. She believes this mix of experiences has given her a unique perspective on the care of acute illnesses.